The use of heavy duty cranes in various industries is quite well known int he art. In recent years, the desirability of having cranes mounted on a truck chassis for movement from one locale to another is well known. Indeed, the art has advanced to the point where extremely large and heavy duty cranes have been mounted on a truck chassis, which include their independent power source such that the truck crane may be driven to any desired location. These types of vehicles re extremely necessary since it is necessary to drive a crane from one locale to another depending upon the location of a construction site.
The typical state of the art truck crane is constructed with the crane mounted on the rear portion of the frame, the front portion of the frame including the truck cab and the engine and drive train of the entire vehicle. Again, typically, the fram eis provided with a series of four outrigger beams such that when the vehicle arrives at the use location, the outrigger beams are extended and the leveling jacks, which are mounted on the end of each outrigger beam in a vertical position, are also extended to engage the ground and raise the entire crane clear of the ground thus effectively supporting the crane on all four outrigger beams and all four leveling jacks. Only in this configuration can the truck crane perform at its rated capacity. However, as is also well known in the art, such vehicles do in fact include the forward portion of the frame, which as indicated previously, contains the truck cab, engine and drive train equipment. For this reason, the vehicle has an elongate configuration and a significant degree of weight. Hence, when the crane is in use, it is not possible to swing any load forward of the front outrigger beams and jacks for the reason that the weight normally contained at that end of the vehicle, plus the weight being lifted by the crane, would have the tendency to weight down the forward end of the entire structure causing the crane to rise off the extended outrigger beams and jacks, and possible cause the tires on the forward portion of the truck crane or steering end to blow out and bend the truck frame forward of the forward outriggers. This particular drawback of the current state of the art vehicles therefore is restrictive with respect to the use of cranes on situs locations, since the crane operator does not have the full 360 degree arc of use of the crane.
In addition, such current state of the art truck cranes are not capable of mobility once at the job site. It will be appreciated that once the truck crane is placed in position, and the outrigger jacks engaged with the underlying ground, the vehicle can no longer be moved when in use. Hence, it is incumbent upon the crane operator to simply lift and lower loads from his single location. The only mobility afforded to the operator is the circumferential path of travel permitted by the circumferential movement of the crane. Hence, it is not possible to move a load from one locale to another by the use of a truck crane. Typically, such mobility is only chieved by transporting to the job site an additional crane, being the crawler type cranes. These cranes are typically hauled to a job site by means of a trailer. The crawler crane is then removed from the trailer, and is then available for work at the job site. However, it will be appreciated that in this instance, the contracting firm engaged in the construction on the job site is required to have two crane vehicles at the same location in order to accomplish the various lifting and travel functions required by a particular construction project. It will again be appreciated that this is a very costly burden on the contractor since he will have double the labor charges as well as double the equipment charges in order to have the advantage of two different types of cranes at the same job site.
Hence, the current state of the art cranes in use have at least two drawbacks with respect to on site usage, those being the limitation in terms of the circumferential path of travel of the crane when employing truck cranes of the type with outrigger jacks as well as the immobility of the truck crane once securely positioned on the job site.
At least one attempt has been made inthe patented art to circumvent the problem of having multiple cranes at a single job site. U.S. Pat. No. 3,929,204 makes an attempt at solving this problem by providing a crane which is mounted on a wheeled trailer, and which the patentee indicates may be converted to a crawler crane on the job site. It will be observed from a view of FIG. 7 of the drawings of the U.S. Pat. No. 3,929,204, that the patentee contemplates the mounting of portable tracks onto the trailer frame by unbolting and removing the outrigger jacks, and installing in the same position the portable crane tracks. It will be observed that in order to accomplish this operation, a separate portable jack must be utilized in order to jack up the trailer frame, which must then be supported with blocks, in order that the outrigger jacks may be removed. Once the outrigger jacks are removed, the crane is manipulated in order to bring the crane tracks into position for mounting onto the mounting apertures where the outrigger jacks were previously located. It will therefore be appreciated that the installation of the portable tracks onto the trailer frame is a rather cumbersome procedure.
In addition, while the subject patent discloses the use of a crane tractor trailer which would be hooked up to the fifth wheel of a typical truck cab, no such equipment presently exists. Hence, while the patentee discusses the advisability of pulling the crane on a wheeled frame to the job site by means of a truck cab, and then converting the crane to a tracked vehicle, the art field has not adopted this procedure since no commercially available units of this description are available.
Finally, the U.S. Pat. No. 3,929,204 discusses the advisability of employing motorized tracks such that each of the tracks would have its independent power source to operate the track. While it is deemed advisable to have motorized tracks, nevertheless, the patent is less than clear on the manner in which an operator can obtain control over the tracks from the crane cab. The Patentee discusses the advisability of removing the hydraulic lines which operate the outrigger jacks, and connecting those to the power sources of each of the tracks, but it is submitted that the main control for the outrigger jacks would simply have an up and down function, which would basically relate to a two position switch. Possibly, this could control forward and reverse, but the operator would have no ability to vary the speed of the tracks. In addition, and even more importantly, the controls which operate the outrigger jacks are usually positioned on the frame adjacent to the outrigger beams, rather than in the cab and as such, the controls are removed from the cab area. Furthermore, those controls are supplied with only an 18 gallon per minute pump which is insufficient to power the tracks for movement. Therefore, even if one produces a crawler crane as suggested by Newell, there is no teaching of how such a crane would be powered. Hence, it is believed that the Patentee has not truly resolved the difficulties and problems encountered in terms of converting a truck crane to a crawler crane.
The present invention is therefore intended to provide a mechanical system for converting presently existing wheeled crane vehicles to a crawler crane, and incorporate within such a system the ability to connect a power source for the tracks to the main crane cab such that the operator has full control over the functions of the crawler crane.